(1) Field of the Invention
The present invention relates to a process for preparing an amino Schiff base or a diamino ketone corresponding thereto.
(2) Description of the Art
It is known that an .omega.-lactam having 4-12 carbon atoms, a linear or cyclic oligomer thereof or a ring-opened polymer thereof may be converted to an .omega.-amino carboxylic acid, which may be used as a starting material for preparing a dimer having the general formula ##STR1## which is known as an amino Schiff base.
Japanese Published Unexamined patent application No. 137974/1975 is a relevant disclosure of such base. The amino Schiff base may be converted to an .alpha., .omega.-diamino alkane which may or may not include an amino group as a side chain. This is indicated, for example, by British Pat. No. 995,482 and U.S. Pat. No. 3,412,156. In order to obtain such an amino Schiff base, an alkali metal hydroxide, alkali earth metal oxide or alkali earth metal hydroxide may be reacted with an .omega.-lactam. This has been proposed in Japanese Published Examined patent application No. 7432/1973, in British Pat. No. 922,275 and in West German Pat. No. 1,131,697.
According to this process, an alkali metal carbonate or an alkali earth metal carbonate is stoichiometrically produced as a by-product. Unless this carbonate is converted to a hydroxide and is reused, the problem remains that the metal hydroxide is consumed in an amount corresponding to the amount of the amino Schiff base produced.
It is suggested in Japanese Published Examined patent application No. 7432/1973 that a so-called recovery process may be provided for converting a metal carbonate to a metal hydroxide and reusing the same.
However, if such a recovery process is resorted to for obtaining an amino Schiff base from an .omega.-lactam, etc., additional costs would be required for recovering alkali metal. Therefore, processes for preparing amino Schiff bases, accompanied by recovery processes, are still in need of drastic improvement.